Poly(sulfoalkyl) gelatin



United States Patent O F 3,539,353 POLY(SULFOALKYL) GELATIN John W.Gates, Jr., and Paul E. Miller, Rochester, N.Y., assignors to EastmanKodak Company, Rochester, N.Y., a corporation of New Jersey No Drawing.Continuation-in-part of application Ser. No. 736,570, June 13, 1968,which is a continuation-in-part of application Ser. No. 364,784, May 4,1964. This application Oct. 7, 1969, Ser. No. 864,556

Int. Cl. C09h 11/00; C08h 1/00; 07n 7/00 US. Cl. 96--114.8 ClaimsABSTRACT OF THE DISCLOSURE New gelatin compounds having sulfoalkylgroups attached to the gelatin molecule, a process for making saidcompounds and photographic elements and emulsions containing saidcompounds are disclosed.

This application is a continuation-in-part of our copending applicationSer. No. 736,570 filed June 13, 1968 now abandoned, which was acontinuation-in-part of copending application Ser. No. 364,784 filed May4, 1964, abandoned as of June 26, 1968.

BACKGROUND OF THE INVENTION Field of the invention The use in thephotographic art of various materials as binding agents forlight-sensitive materials such as silver halides is well known. Whilemany hydrophilic polymers have been used as suspending media forlight-sensitive materials and as extenders, no substance has been usedwith greater photographic acceptability than gelatin. The term gelatin,as will be readily understood to those skilled in the art, defines amanufactured product from collagen, which is a naturally occurringfibrous protein and a major protein component of skin, bone and certainother animal tissue. It has long been known that, depending upon itssource, gelatin possesses both various desirable and undesirablephysical and chemical characteristics when used in photographic elementsand, more particularly, in light-sensitive emulsions. For variousreasons, gelatin derived from cattle, and most desirably from cattlebone and hides, is most useful for photographic purposes because bindedscomprising said cattle-derived gelatin are relatively permeable todeveloping solutions, have good physical characteristics, permitreasonably short processing times, and form silver halide emulsionswhich exhibit higher speed and higher contrast in comparison to gelatinderived from other sources.

While it would be economically advantageous to utilize in photographicelements generally, and more particularly ice in high speed, negativeemulsions, gelatin derived from skins and bones of animals other thanthe high priced and invariably imported cattle, heretofore this has notbeen possible. For example, the use of pig gelatin has not previouslybeen satisfactory because of desensitizing effects and the restraint ofphysical development in photographic use of said pig gelatin. Theseobjectionable results are even more pronounced in use with developershaving a high salt content, for example. The photographic art would,therefore, be greatly enhanced by new gelatin compounds which areeconomically, commercially and photographically acceptable replacementsfor cattle gelatin.

SUMMARY OF THE INVENTION This invention relates to new gelatin compoundshaving sulfoalkyl groups attached to the gelatin molecule. Saidcompounds can be derived from pig and more particularly pigskin and arecharacterized by specific physical and chemical properties whichdistinguish them from all other pigskin gelatins.

These new gelatin compounds are particularly useful in photographicelements and as binders in light-sensitive photographic emulsions.

A significant feature of this invention is that our new sulfoalkylgelatins possess photographic, sensitometric and physical propertiesheretofore thought available only through use of cattle-derived gelatin.By a process of chemically modifying pig gelatin, we have successfullyintroduced new groups into the complex gelatin polymer molecule which sounexpectedly and dramatically change the characteristics of saidmolecule that the restraint to physical development can be completelyovercome and photographic acceptability achieved.

In one aspect our invention comprises providing a chemically modifiedpig and pigskin gelatin whose inherent detrimental characteristics, forexample, its development restraint, have been removed while its otherdesirable physical characteristics have been retained within desirableand reproducible limits, as illustrated in Charts I and II hereafter.

By restraint to physical development we mean an inhibition by an exposedphotographic emulsion to respond to development within the timedesirably required to produce a visible image with corresponding goodsensitometric effects.

Accordingly, it is an object of our invention to provide newphotographic elements comprising chemically modified gelatins frompreviously less desirable sources. It is another object of our inventionto provide processes for chemically modifying pig gelatin by introducingsulfoalkyl groups into gelatins complex polymeric molecule.

It is another object of our invention to provide poly- (sulfoalkylated)gelatin having improved physical and chemical characteristics ascompared to the parent gelatin from which it is derived.

Other objects of this invention willbecome apparent from an examinationof the specification and claims that follow.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In accordance with ourinvention, the above objects are attained with new chemically modifiedgelatin. Said gelatin is characterized, in part, by being chemicallycom- 3 bined with a plurality of sulfoalkyl units, that is, alkyls of 3to 4 carbon atoms. Said sulfoalkyl units are chemically united inrecurring numbers on the gelatin macromolecule by reacting upon gelatinin alkaline solution with an alkyl sultone.

These repeating sulfoalkyl units impart generally decreased developmentrestraining properties to light-sensitive emulsions such as pig gelatinemulsions containing said units and corresponding decreaseddesensitizing effects in concentrations of greater than about 3 byweight of gelatin. In concentrations of about 4 to about 6% by weight,the resistance to development restraint is completely overcome, i.e.,the gelatin is substantially photographically inert to physicaldevelopment restraint.

Although gelatin is a naturally occurring protein composed of knownalpha-amino acids, the composite structural arrangement and position ofsaid acids in the gelatin molecule is largely unknown and at bestspeculative.

One of these alpha-amino acids present in the gelatin molecule is Lysineand is known to have a reactive omega-amino functional group substitutedthereon.

Thus, While the highly complex gelatin molecule contains a multiplicityof reactive sites, some of which are known and identifiable, others areunknown and to date are unidentifiable since factors which contribute tothe ultimate reactivity of a gelatin molecule-contained alphaamino acid,are contingent upon said acids unknown structural relationship to otheralpha-amino acids present in the gelatin molecule.

Therefore, it can be fairly said that the present state of chemical andbiochemical analytic technology has not yet advanced to the point wherea determination of the range of reactive sites of the gelatin moleculecan be absolutely determined and efforts to most specifically designateboth all of the reactive sites and their range whereon sulfoalkylationoccurs have been unsuccessful and the source of some speculation. (SeeMees, Theory of the Photographic Process, MacMillan, 3rd edition, pages4554.)

Consequently, while it is possible that not all of the reactive site canbe presently determined due to the state of the art, we have,nevertheless, unequivocally chemically modified gelatin as shownhereafter on both the lysine and hydroxylysine sites. Example 3, whichfollows, describes the characteristics of the chromatograms of themodified and unmodified gelatin. The comparative data of these examplesshow with certainty that the poly sulfoalkylation of gelatin occurssubstantially on those two recurring alpha-amino acid sites. Further,said poly sulfoalkylation appears to occur on the epsilon-amino group ofeach of said amino acid sites. By poly it will be understood by thoseskilled in the art to mean not only the numerous and substantialsulfoalkylation of these recurring sites but also the additionaldisubstitution of many of said recurring sites. Further by the use ofthe term recurring one skilled in the art will also understand this tomean repeating in a random fashion and not necessarily in an ordered andregularly repeating manner. Gelatin is specifically characterized alongwith other physical properties by its amino acid sites and compositionsthereof, and each of these is subject to very small variations aftermodification of the molecule as shown herein. We have thus producedspecific and reproducible changes by the chemical modification of polysulfoalkylation, which changes are used to identify and fingerprint ournew compounds. These gelatin compounds are characterized in terms oftheir jelly strength, viscosity, color clarity, isoelectric point,lysine and hydroxylysine content and degree of substitution andsulfoalkylation.

In particular a comparison of the data, representing the variouschromatograms of both pure gelatin and gelatin chemically modified bysubstantially sulfoalkylat ing the lysine and hydroxylysine sites,indicates with marked clarity that the sulfoalkylysine sites, indicateswith marked clarity that the sulfoalkylation produces new peaks on saidamino acid sites to the substantial exclusion of all other amino acidsites. It is seen by comparing the differential of the lysine andhydroxylysine concentration in the various samples of plain gelatin andpoly(sulfoalkylated) gelatin that We have efiected sulfoalkylation onthe lysine site in ranges from about 30 to about and on thehydroxylysine site from about 50 to about The level of each amino acidpresent in the chemically unmodified gelatin remains relatively constantat about .281 micromole per milligram of lysine and about .062 micromoleper milligram of hydroxylysine. The degree of sulfoalkylation recordedis thus dependent upon the initial values of the unmodified gelatin.

These various characterizing terms are well known in the art and can bedetermined in a variety of ways employing suitable means. For example,viscosity can be determined by the rolling ball test, which test employsa viscosimeter to determine the length of time in seconds required by ametal ball to fall through a given distance of a solution of gelatin.This can also be measured equally Well in terms of inherent viscosity inwater at a concentration of 0.25 gram per 100 milliliters of solution at25 C. Isoelectric point can be determined conveniently employing mixedresins according to the procedure of Janus, Kenchington and Warddescribed in Research, volume 4, page 247 (1951). Color clarity is themeasured amount of light transmitted through various solutions and ratedon a photometer, for example, a lumitron. A test for determining jellystrength is described hereafter.

A preferred embodiment of our invention comprises poly(sulfoalkyl)gelatin being characterized by having the following properties:

Shom jelly strength of about 200 to about 285;

Color clarity of about to about Isoelectric point of about 4.3 to about5.7;

Viscosity of about 9.4 to about 12.7;

Lysine micromoles per milligram of about 100 to about 200; and

Hydroxylysine micromole per milligram of about .015

and about .025.

The novel sulfoalkylated polymers of our invention can be derived byreacting gelatin, such as pig and preferably pigskin and pig bonegelatin, With a suitable sulfoalkylating compound. This reaction is mosteffective in a wide pH range but it is preferred that said pH bealkaline, that is, greater than about 7 and preferably about 9 to about11. This reaction between gelatin, such as pig gelatin, having inherentundesirable sensitometric and photographic characteristics, and asulfoalkyl compound such as an alkyl sultone, for example, a propane orbutane sultone, can be efiected equally well under either warm or coldconditions. In one preferred embodiment, the modified gelatin of ourinvention is pre pared by first plumping gelatin into cold water (thatis, having a temperature of less than about 15 C.), raising thetemperature to about 50 C. thereby melting the gelatin. The pH is thenadjusted in the resulting solution or suspension to about 10.5 with analkaline substance, such as sodium hydroxide, potassium bydroxide andthe like. Alkyl sultone, previously dissolved in a suitable solvent suchas acetone, alcohol, benzene and the like, is added preferably withagitation and the pH is maintained at greater than about 7 andpreferably at about 9.5 to about 10.5. The chemically modified gelatinis conveniently recovered by acidifying the solution to a pH of lessthan about 6, for example, by the addition of dilute sulfuric acid,dilute hydrochloric acid and the like. In the final steps, thepoly(sulfoalkyl) gelatin is then chilled, noodled and Washed with coldwater as is well known to those skilled in the gelatin art.

Another preferred embodiment of our invention comprises sulfoalkylatinggelatin under cold conditions and is effected by plumping flakes ofgelatin, that is, pig gelatin, for example, into cold water (forexample, distilled water) having a temperature of less than about 15 C.The pH is adjusted to about 9.5 to about 10 such as by the addition ofmagnesium oxide, for example, and the alkyl sultone, in water, is addedto the plumped gelatin flakes. The temperature is depressed, forexample, to about 7 C. for about four days. The poly(sulfoalkyl) gelatinthus prepared is washed to remove the alkaline substance, for example,magnesium oxide, and after leaching with dilute acetic acid, forexample, is melted, filtered, chilled and dried.

The characteristics of these sulfoalkyl gelatins produced by eithermethod are very similar, as indicated before, except that the jellystrength of the product obtained in the absence of heat, that is, bycold process, understandably exhibits a slightly higher jelly strength.By jelly strength is meant the firmness of resistance to deformation ofa gel prepared under standard conditions. This is determined by use of aBloom Gelometer and the values are customarily referred to as Bloomjelly strengths. By definition, this is the weight in grams required toproduce by means of a plunger 12.7 mm. in diameter a depression of 4 mm.in the surface of a gel of a concentration of 6%% by weight, measured at10 C.i0.1 C. for a period of 16-18 hours (see Photographic Gelatin,Croome and Clegg Focal Press, London 1965). Shoom jelly strength is amodification of the above valuation in that the concentration of thegelatin is more dilute, that is, reduced to about 6.1% by weight. In allother respects, these jelly strength tests are the same. Forphotographic purposes, a high jelly strength is desirable, that is, atleast 150 and preferably between 200 and 295. Unmodified pigskin gelatinhas a Shoom jelly strength of about 280 to about 260 but is possessed ofheretofore unalterable and undesirable development restraint, andtherefore is generally unsuitable in photographic applications.

When combined in photographic elements and in lightsensitive silverhalide emulsions, our poly(sulfoalkyl) gelatins can contain photographicaddenda such as gelatin plasticizers, coating aids, and hardeners suchas aldehyde hardeners, e.g., formaldehyde, mucochloric acid,glutaraldehyde bis(sodium bisulfite), maleic dialdehyde, azirdines,dioxane derivatives, oxypolysaccharides, vinylsulfonyl ethers and thelike. Spectral sensitizers which can be used are the cyanines,merocyanines, complex (trinuclear) cyanines, complex (trinuclear)merocyanines, styryls, and hemicyanines. Sensitizing dyes useful insensitizing such emulsions are described, for example, in 11.5. Pats.2,526,632 of Brooker et al. issued Oct. 24, 1950, and 2,503,776 ofSprague issued Apr. 11, 1950. Developing agents can also be incorporatedinto the silver halide emulsion if desired or can be contained in acontiguous layer. Various silver salts can be used as the sensitive saltsuch as silver bromide, silver iodide, silver chloride or mixed silverhalides such as silver chlorobromide or silver bromoiodide. The silverhalides used can be those which form latent images predominantly on thesurface of the silver halide grains or those which form latent imagespredominantly on the surface of the silver halide grains or those whichform latent images inside the silver halide crystals such as describedin US. Pat. 2,592,250 of Davey ct al. issued Apr. 8, 1952.

The silver halide emulsion layer of a photographic element containingthe poly(sulfoalkyl) gelatins of our invention can contain combinedwith, and in addition to, our gelatins any of the hydrophilic,water-permeable binding materials suitable for this purpose. Theconcentration of our poly(sulfoalkyl) gelatins can vary from more thanabout to about 90%, by weight, of binding agent, e.g., gelatin used, andpreferably is present in a concentration range of about 40 to about 75%by weight of total binder. Suitable materials include other gelatin,modified or unmodified, colloidal albumin, polyvinyl compounds,cellulose derivatives, acrylamide polymers, etc. Mixtures of theselatter binding agents can also be used in combination with oursulfoalkyl gelatins.

The binding agents for the emulsion layer of the photographic elementcan also contain dispersed polymerized vinyl compounds. Such compoundsare disclosed, for example, in U.S. Pats. 3,142,568 of Nottorf issuedJuly 28, 1964; 3,193,386 of White issued July 6, 1965; 3,062,674 ofHouck et al. issued Nov. 6, 1962; and 3,220,844 of Houck et al., issuedNov. 30, 1965; and include the water-insoluble polymers of alkylacrylates and methacrylates, acrylic acid, sulfoalkyl acrylates ormethacrylates and the like.

In addition, the novel poly(sulfoalkyl) gelatins of our invention areparticularly useful in photographic elements and layers, for example, invarious layers or protective coatings, and layers such as overcoats,antihalation layers, interlayers, and the like and in emulsion layerscomprising light-sensitive materials as set forth herein.

The silver halide emulsion of a photographic element containing thechemically modified gelatins of our invention can be coated on a widevariety of supports. Typical supports are cellulose nitrate film,cellulose ester film, polyvinyl acetal film, polystyrene film,poly(ethylene terephthalate) film and related films or resinousmaterials as well as glass, paper, metal and the like. Supports such aspaper which are coated with alpha-olefins polymers, particularlypolymers of alpha-olefins containing two or more carbon atoms, asexemplified by polyethylene, polypropylene, ethylene-butene copolymersand the like can also be employed.

The speed of the photographic emulsions containing the new gelatins ofour invention can be further enhanced by including in the emulsions avariety of hydrophilic colloids such as carboxymethyl protein of thetype described in US. Pat. 3,011,890 of Gates et al. issued Dec. 5,1961, and polysaccharides of the type described in Canadian Pat. 635,206of Koller et al. issued Jan. 23, 1962.

Photographic elements and emulsions containing the gelatins of theinvention herein can also contain speedincreasing compounds such asquaternary ammonium compounds, polyethylene glycols or thioethers.Frequently, useful effects can be obtained by adding the aforementionedspeed increasing compounds to the photographic developer solutionsinstead of, or in addition to, the photographic emulsions.

Photographic elements containing our new gelatins can be used in variouskinds of photographic systems. In addition to being useful in X-ray andother non-optically sensitized systems, they can also be used inorthochromatic, panchromatic and infrared sensitive systems. Thesensitizing addenda can be added to photographic systems before or afterany sensitizing dyes which are used.

Silver halide emulsions containing the sulfoalkyl gelatins of theinvention can be used in color photography, for example, emulsionscontaining color-forming couplers or emulsions to be developed bysolutions containing couplers or other color-generating materials,emulsions of the mixed-packet type such as described in US. Pat. 2,698,-794 of Godowsky issued 1 an. 4. 1955; in silver dye-bleach systems; andemulsions of the mixed-grain type such as described in US. Pat.2,592,243 of Carroll et al. issued Apr. 8, 1952.

Silver halide emulsions and elements containing the gelatins of theinvention can be sensitized using any of the well-known techniques inemulsion making, for example, by digesting with naturally active gelatinor various sulfur, selenium, tellurium compounds and/or gold compounds.The emulsions can also be sensitized with salts of noble metals of GroupVIII of the Periodic Table which have an atomic weight greater than 100.

Silver halide emulsions and elements containing the sulfoalkyl gelatinsof our invention can be used in diffusion transfer processes whichutilize the undeveloped silver halide in non-image areas of the negativeto form a positive by dissolving the undeveloped silver halide andprecipitating it on a silver layer in close proximity to the originalsilver halide emulsion layer. Such processes are 7 described in US.Pats. 2,352,014 of Rott issued June 20, 1944; 2,543,181 of Land issuedFeb. 27, 1951; and 3,020,- 155 of Yackel et al. issued Feb. 6, 1962. Theemulsions can also be used in diffusion transfer color processes whichutilize a diffusion transfer of an imagewise distribution of developer,coupler or dye, from a light-sensitive layer to a second layer, whilethe two layers are in close proximity to one another. Silver halideemulsions and elements containing the gelatins of the invention can beprocessed in stabilization processes such as the ones described in US.Pat. 2,614,927 of Broughton et a1. issued Oct. 21, 1952, and asdescribed in the article Stabilization Processing of Films and Papers byH. D. Russell et al. in P.S.A. Journal, Photographic Science andTechnique, vol. 16B, October 1950.

The gelatins of this invention can be incorporated to advantage duringmanufacture in silver halide emulsions and elements representing thevariations described.

Combinations of all the above-mentioned addenda can be used if desired.

The following examples are included for a further understanding of theinvention.

EXAMPLE 1 900 grams of pigskin gelatin are dissolved in 9 liters ofdistilled water at 50 C. Sodium hydroxide is added so as to adjust thepH of the solution to 10.5. Added with stirring are 27 grams (3% byweight of the pig gelatin) of 1,3-propanesultone in solution in 75milliliters of acetone. Stirring is continued for 30 minutes with the pHof the solution being maintained at 10.0 by addition of sodium hydroxideas needed. Thereupon, the pH of the solution is lowered to 6.0 by addingdilute sulfuric acid. The resulting chemically modified gelatin solutionis chilled, noodled, Washed and dried in customary fashion.

EXAMPLE 2 Portions of the above chemically modified pigskin gelatin arechromatographically analyzed by a method of the type described by Mooreand Stein in J. Bio. Chem., 192, 663-681 (1951). This procedure is asfollows:

Each sample is dried at 60 C. in vacuum for 16 hours. A sample of eachof about 4 milligrams weight is weighed S exactly and is hydrolyzed in5.5 N hydrochloric acid for 22 hours at 110 C. in a sealed system. Eachis evaporated to dryness in a vacuum desiccator and is dissolved at pH2.2 in a citrate buffer A (pH 2.2) and is diluted to 5 milliliters withcitrate buffer A. One milliliter of the diluted solution is placed on awater jacketed ion exchange column containing sulfonated polystyreneresin (Beckman type B resin), said column being 50 centimeters long and0.9 centimeter in diameter. The equipment used is a Beckman model 120 Bamino acid analyzer.

Then the column is eluted with citrate buffer B (pH of 3.28). The columntemperature is in itially held at 30 C. changing to 50 C. aftermilliliters of eluent is passed through the column. Citrate buffer C (pH4.5) is then used as the eluent and during the course of the elution,the column eluent is automatically mixed with minhydrin reagent and thestream is put through a heated reaction coil at C. to developcharacteristic blue colors for each amino acid. The colors formed aremonitored in a Stream Colorimeter whose output is recorded on a stripchart recorder. This gives a separation of the acidic and neutral aminoacids.

For the purpose of separating the basic amino acids, second 1 milliliteraliquot portions of each of the hydrolyzed samples in solution incitrate buffer A are taken and placed on a jacketed column of 0.6centimeter diameter and 10 centimeters length which contain sulfonatedpolystyrene resin (Beckman type 15A). The sample is eluted with citratebuffer D (pH 5.28). After passing 60 milliliters of eluent through thecolumn the basic amino acids are completely separated. During the courseof the elution, the column eluent is automatically mixed with ninhydrinreagent, the stream is put through a heated reaction coil at 100 C. andthe colors formed are monitored in a Stream Colorimeter whose output isrecorded on a strip chart recorder, the time value for which is setforth on the axis of the ordinate, reading from left to right. Thecitrate buffers are principally composed of aqueous solutions of amixture of sodium citrate and hydrochloric acid whose proportions areadjusted to supply the desired pH.

The results obtained in this and the other following examples whichemploy various degrees of sulfoalkylation are tabulated as follows:

Nominal percent of Hydroxy- 71 116 32 sulfopropyl Hydroxylysine minuteLysine minute minute Sum Sample number substitution lysine 1 decrease 1peak 1 Lysine I decrease 1 peak I peak 1 116+32 1 N0. 1: N L10fi-195-1.0 062 281 L1061953 5 021 O41 036 175 .106 085 030 o. 4:

LNG-1954 7 017 O45 042 123 158 101 029 o. 5:

L106-156-1 3 0&6 018 039 193 O71 069 008 .073 o. 8:

L106-156-2 4 032 032 028 130 125 070 O13 088 N0. 9:

L106-156-3 5 028 036 O41 123 141 124 024 14 1 N0. 10:

L106-l56-4 6 023 0&1 O41 101 163 137 037 o. 11:

1 All valuw in mieromoles per milligram. 2 Not available.

Photocopies of the chromatograms of the samples of Example 2 and otherexamples which follow hereafter show the appearance of a new peak ateach of the elution times of about 71 and 116 minutes. When each ofthese peaks is compared to the percentage substitution, they indicate alinearity in the to about range and a leveling off in the 7% to aboutrange. The lysine content decreases linearly up to about 7% or, to avalue of .120 to .193 micromole per milligram. This new peak at eachelution time appears to represent a primary sulfoalkylation of saidreactive receiving sites.

A barely visible third new peak is observed at 32 minutes in some of thechromatograms and appears to be due to additional new sulfoalkylation asthe disubstitution of sulfoalkyl moieties on already monosulfolakylatedamino acid sites.

This data clearly illustrates that samples 25 and 7-11 arepoly(sulfoalkylated) gelatins, the chemically modified reaction productbetween propanesulfone and pigskin gelatin.

EXAMPLE 3 Example 1 is repeated but using 36 grams (4% by weight) of1,3-propanesultone rather than the 27 grams.

EXAMPLE 4 Example 1 is repeated but 45 grams (5% by weight) of1,3-propanesultone are used.

EXAMPLE 5 Example 1 is repeated but 54 grams (6% by weight) of1,3-propanesultone are used.

The gelatin is chilled, noodled, washed and dried in the usual manner.

EXAMPLE 8 The preceding example is repeated but 15 grams of 2,4-butanesultone are added.

EMMPLE 9 Example 7 is repeated but grams of 2,4-butanesultone are added.

In the following two charts, we set forth various unique physical andphotographic properties and identifying characteristics of ourchemically modified gelatins, of Examples 1 and 36, as compared withtheir parent pigskin gelatin and the previously preferred cattle bonegelatin. It is seen, for example, in Chart I that, while the parentpigskin gelatin possesses excellent jelly strength, its restraint tophysical development (shown in Chart II) renders it photographicallyunacceptable, shown in part by high relative speed.

The chemically modified sulfoalkylated gelatins, however, provideexcellent sensitometric results and particularly good developmentrestraint control within the time required for the various commerciallyavailable developers. In particular, our poly(sulfoalkyl) gelatincompares most favorably with cattle bone gelatin and in preferred rangesis inert to physical development restraint.

The following chart representing 6.1% by weight of the various gelatinsolutions gives the unique physical properties and characteristics ofthe chemically modified gelatins obtained in Examples 1, 3, 4, 5, and 6(modified by sulfoalkylation to the extent as shown by percentages) ascompared to untreated igskin gelatin and other gelatin.

CHART I [Physical proprties] Jelly strength (shoom value in C olorIsoelectric Gelatm used Viscosity grams) clarity point Cattle bonegelatin 11. 9 278 80-98 4. 9 Parent pigskin gelatin 11. 8 205 87-98 8.8Example 1 10. 4 246 87-100 5. 7 Example 4 10. 2 236 88-100 5. Example 510.0 222 86-99 4. 0 Example 6 9. 4 200 90-100 4. 3 Example 7 12. 7 25587-100 5.

EXAMPLE 6 EXAMPLE 7 200 grams of pigskin gelatin are plumped and meltedin 2 /2 liters of distilled water at 50 C. Sodium hydroxide is added toadjust the pH to 10.5. 10 grams of 2,4-butanesultone in solution inacetone are stirred into the solution. The solution is held for minuteswith occasional addition of NaOH to maintain the pH at 10.0. Thereuponthe pH is lowered to 6.0 by adding dilute sulfuric acid.

The gelatins obtained by the various examples are evaluatedphotographically by using the various modified and unmodified gelatinsrespectively as binders in a high speed silver bromoiodide (6 molepercent iodide) photographic emulsion. These various emulsions arecoated on a cellulose acetate film base at a coverage of 540 milligramsof silver and 1225 milligrams of gelatin per square foot in whichoperation the coatings after application are chill set and dried. Eachfilm strip is exposed on an Eastman Sensitometer Type IB and acontinuous step wedge is used. The films are processed for the timesspecified in the following tables in Kodak Developer DK50 or inDeveloper D19 and are fixed for 5 minutes in Kodak Fixing Bath F5,washed and dried. The properties of these films when freshly processedand in some cases after a one-week incubation period holding at 50%relative humidity and 120 F. temperature are as follows:

CHART II 1 week incubation Fresh 5 DK-50 5 D 5 Fresh 12 DK-50 Fresh 4D-19 Relative Relative Relative Relative Gelatin Used speed S Fog speedS Fog speed S Fog speed S Fog Cattle bone gelatin 100 1. 17 09 0. 8146 1. 23 22 80 1. 15 06 Parent pigskin gelatin 71 1. 02 06 54 0. 94 1263 1. 25 18 54 1. 04 05 Example 1 80 l. 17 12 54 0.77 52 83 1. 10 2265 1. 07 10 Example 4 1.08 .10 68 0. 77 .36 129 1.10 18 94 1. 05 08Example 5 129 1. 15 11 78 0.93 40 155 1. 20 19 102 1. 15 10 Example 6 1.27 12 148 1. 20 20 102 1. 10 10 Example 7 120 1. 38 12 105 1. 41 10 Theinvention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

We claim:

1. Poly(sulfoalkyl) gelatin containing recurring lysine sites of whichabout to about are sulfoalkylated and hydroxylysine sites of Which about50 to about are sulfoalkylated, said gelatin being poly(sulfoall;ylated) substantially on the epsilon amino groups of said lysine andhydroxylysine sites.

2. Poly(sulfoalkyl) gelatin of claim 1 being characterized by having thefollowing properties:

Shoom jelly strength of about 150 to about 285; Color clarity of aboutto about Isoelectric point of about 4.3 to about 5.7; Viscosity of about9.4 to about 12.7; Lysine micromoles per milligram of about 100 to about200; and Hydroxylysine micromoles per milligram of about .015 to about.030. 3. The poly(sulfoalkyl) gelatin of claim 1 in which said alkyl ispropyl.

4. The poly(sulfoalkyl) gelatin of claim 1 in which said alkyl is butyl.

5. A photographic element comprising a support and layer containing thepoly(sulfoalkyl) gelatin of claim 1.

6. A photographic gelatin silver halide emulsion comprising thepoly(sulfoalkyl) gelatin of claim 1.

7. The poly(sulfoalkyl) gelatin of claim 1 derived from pig collagen.

8. A method of preparing a gelatin derivative which comprises reactingupon gelatin in alkaline solution with an alkyl sultone, the alkyl beingof 3 to 4 carbon atoms.

9. The method of claim 8 in which said gelatin is pigskin gelatin andsaid alkyl sultone is propane sultone.

10. The method of claim 8 in which said gelatin is pigskin gelatin andsaid alkyl sultone is butane sultone.

References Cited UNITED STATES PATENTS 12/1965 Vrancken et al 96947/1969 Young 2608 US. Cl. X.R. 260-ll7

